- Fix misconfigured ipsecmod hook causing path name

similarity with other file. The ipsecmod is changed for
  exec of the hook. The ipsecmod hook, if a script, has to
  start now with a line like `#!/bin/sh`. Thanks to Qifan
  Zhang, Palo Alto Networks, for the report.

testdata/ipsecmod_hook.sh

@@ -1,2 +1,3 @@
+#!/bin/sh
 echo " ---[ IPsec external hook FAIL; only care if ipsecmod-strict: yes ]---"
 exit 1